Hyperammonemia associated with several rare inherited disorders frequently causes mental retardation, developmental disabilities and death. The overall goal of this study is to investigate the short-term efficacy and safety of the orphan drug, N-Carbamyl-L-glutamate (Carbaglu®, abbreviated as NCG), for the treatment of hyperammonemia in rare inherited disorders: carbamyl phosphate synthetase I (CPSI) deficiency, NAGS deficiency, ornithine transcarbamylase (OTC) deficiency, propionic acidemia (PA) and methylmalonic acidemia (MMA).